The present invention relates to a bleed device for hydraulic circuits, particularly for hydraulic brake circuits for vehicles that does not require loosening of the hydraulic drain plug.
As is known, in hydraulic brake systems, normally on each brake, there is provided a bleed device or drain device which, in most cases, is made in the form of a threaded plug, screwed into an aperture of the hydraulic brake circuit and having a conical end which, when the plug is tightened in the aperture, bears on a seat of the aperture and acts as a valve member, or obturator, or a stopper for the aperture. In order for the required degree of sealing to be achieved, the stopper must be tightened against the seat with a predetermined force. This tightening, at the time of assembly of the brake, is carried out correctly by way of torque spanners.
A drain duct or bleed duct is formed axially in the plug, and can be connected hydraulically to the hydraulic circuit when the plug is slackened in the aperture. The first filling of the hydraulic brake circuit is normally carried out under a vacuum, and on this occasion it is not necessary to bleed the hydraulic circuit by slackening the bleed plugs. Subsequently, when brake maintenance operations are carried out, it is possible to bleed the brake circuit by connecting the bleed duct to a small tube which drains into a bleed vessel, by pressurizing the hydraulic circuit with the plug closed, slackening the plug so that air bubbles are expelled through the bleed duct, and then tightening the plug again to close the hydraulic circuit. The operation is repeated several times for each brake, until the air or other compressible gases, which would adversely affect the operation of the brakes, are completely bled from the hydraulic circuit.
On these occasions, it is possible that the optimal tightening force may not be restored for some of the bleed plugs, or, which is even worse, that they will not be tightened at all. A plug which is not properly tightened is potentially subject to the risk of further slackening as a result of the vibrations to which the brake is subjected in use, and may even be slackened completely, with disastrous results for the efficacy of the hydraulic brake circuit. This problem is even more serious in sports vehicles, since these are subject to continual adjustment operations, very frequently in conditions of stress and excitement which can cause even the most skilled workers to make possible errors.
To prevent the accidental unscrewing of the bleed plugs, it has been suggested that an arrangement for stopping the rotation be used, which meet the requirements, even if the bleed plug is not completely tightened, but these have the disadvantage of a considerable constructional and operational complexity.
A further disadvantage to which conventional bleed devices are subject is that they permit the infiltration of any dirt and/or water which may be present, thus contaminating the brake fluid, even if the plugs are provided with protective caps.
The present invention solves the longstanding and unresolved need for a bleed device that is structurally and functionally designed to provide rapid bleeding of hydraulic circuites while avoiding the disadvantages of known bleed plugs. For example, one embodiment of the present invention has a bleed duct comprising a one-way check valve that is closed during normal operation of the hydraulic circuit, but is capable of being opened during bleeding of the hydraulic circuit without loosening the bleed device from the hydraulic circuit.